In 2007 Singler led South Medford to its first-ever state basketball championship, winning 58–54 over defending champion Lake Oswego and national standout Kevin Love.[3] A year earlier Love and Lake Oswego had defeated Singler and South Medford for the state championship.

Singler was a member of the Legends AAU team, along with future UCLA player Kevin Love, and participated in many prestigious all-American camps, including the Nike All-American Camp (Indianapolis), the Nike Peach Jam (Augusta), and the Main Event (Las Vegas).

Singler started at power forward as a freshman, and finished the 2007–08 season with averages of 13.3 points per game and 5.9 rebounds per game, helping lead Duke to a 28–6 record. Singler put to rest any speculation that he might enter the 2008 NBA draft, saying:

I didn’t give the NBA any thought, I know I’m not ready. I need to mature both physically and mentally. I want to get stronger and quicker, and I want to work on learning how to play the game. I’m at a great place for that.[5]

In January 2009 he had a career-high 16 rebounds against Georgetown,[6] a game in which Duke won 76-67. Singler ended the 2009 season as the top scorer for Duke.[7] At the end of the season Singler was averaging a team high 16.5 points per game in just 37 games played.[8]

In February 2010 Singler scored a career-high 30 points against Georgia Tech, hitting a career-high 8 three-pointers in 10 attempts.[6] In the ACC Tournament Final (playing Georgia Tech again), he hit a career-high 14 free throws.[6]

On March 28, 2010, in an Elite Eight NCAA game, as Duke beat Baylor and advanced to the Final Four, Singler (667 points), Jon Scheyer (690 points), and Nolan Smith (628 points) became the second trio in the history of the school to score at least 600 points each in the same season. Jason Williams, Carlos Boozer, and Mike Dunleavy, Jr. first accomplished that feat for Duke in 2001–02.[9] Singler scored 19 points in the national championship game to reach 707 for the season, joining Scheyer (728) as the two became the second duo in Duke history to each score over 700 points in one season,[10] following in the footsteps of Jason Williams (841) and Shane Battier (778), who did so for Duke's 2001 national championship team.[10]

Through the 2009–10 season, Singler was also 6th on Duke's all-time list in offensive rebounds (272), and 7th in defensive rebounds (490).[11] For the season he averaged 17.7 points and 7.0 rebounds per game.[12] He was 3rd in the ACC in 3-point field goal percentage (.399), 4th in scoring, 3-point field goals made (2.1 per game; his 8 against Georgia Tech were the most in the ACC in a single game for the season), and minutes (35.9 per game), and 7th in free throw percentage (.798).[13]

Singler was instrumental in Duke winning its fourth national championship; he was named NCAA Final Four Most Outstanding Player after averaging 20.0 points, 9.0 rebounds and 3.5 assists per game in wins over West Virginia and Butler. Scheyer called him "the toughest player I've ever played with."[14]

Following the national championship, Singler considered entering the 2010 NBA draft,[15] but ultimately decided to return for his senior season at Duke.[16] Singler was named the pre-season Atlantic Coast Conference player of the year, pre-season first team All-ACC, and was named a pre-season first team All-American. On November 27, 2010 Singler tied his career high 30 points against his brother E. J. Singler and the Oregon Ducks. Singler was also voted to the Atlantic Coast Conference first team. For the 2010–2011 season, Singler averaged 16.9 points, 6.8 rebounds, and 1.6 assists in 34.8 minutes per game for the Blue Devils.[17] The Blue Devils were eliminated in the Sweet 16 in the tournament against the Arizona Wildcats by the score of 93-77. Singler had 18 points in the defeat.[18]

Singler was selected with the 33rd overall pick in the 2011 NBA draft by the Detroit Pistons.[19] On August 23, 2011, he signed with CB Lucentum Alicante of the Liga ACB. The contract had an NBA out-clause for when the NBA lockout ended.[20] In his Liga ACB debut, he won the MVP of the first match day with 23 points, 4 rebounds and 3 assists. Following the conclusion of the lockout, Singler exercised his option to leave the club. He chose to join Real Madrid on November 30, 2011 after the two clubs agreed on a transfer fee.[21] In 10 appearances with Alicante, Singler helped them win 7 games while averaging 14.4 points, 3.4 rebounds and 1.1 steals. He went on to help Real Madrid defeat Barcelona to win the 2012 Spanish King's Cup.[22]

On July 9, 2015, Singler re-signed with the Thunder.[26] For much of the Thunder's first two months of the 2015–16 season, Singler was a seldom-used, third-string forward off the bench. Between November 24 and New Year's Eve, Singler sat out eight games and twice played less than 60 seconds. Over the team's first 32 games of the season, Singler had made just six of his 31 three-point shots.[27] He began to receive more game time in mid-January, and on January 20 against the Charlotte Hornets, Singler scored a season-high 11 points and hit 3-of-3 from three-point range.[28]